1. Field of the Invention
The present invention relates generally to a device for use in vacuum casting and more specifically to a combination vacuum chamber and casting flask. This device is used in the process known as the lost wax method for producing precision castings which is often used in the dental and jewelry fields. This process begins with the pouring of an investment slurry into a flask which contains a wax model of the desired end product. Once the slurry has hardened, the flask and investment are subject to a burn-out treatment to thereby burn away the wax model. The flask is placed over a vacuum source in order to pull air through the hardened investment. Molten metal is then poured into the void left by the wax model, and is pulled into extreme portions of the void. The molten metal is then allowed to solidify and cool.
2. Description of the Prior Art
Various types of casting flasks have been proposed in the prior art. For example, in U.S. Pat. No. 1,429,322 to Brophy, a casting flask is provided with holes in its side walls to thereby aid in the drying and burning out and heating of the investment compound. A sleeve is provided to slide over the flask so as to allow the investment slurry to be poured into the flask without pouring out through the holes. U.S. Pat. Nos. 1,473,278 and 1,490,090 to Burns disclose receptacles to hold different sized casting flasks. U.S. Pat. No. 3,780,787 to Rasmussen discloses a method of vacuum investment casting in which the investment is removed from the flask before molten metal is poured therein. The investment is cast with a shoulder portion which rests upon the upper edge of a vacuum chamber during vacuuming. The book by Murray Bovin entitled "Centrifugal or Lost Wax Jewelry Casting" discloses at pages 80-81, FIGS. 180-181, a prior art vacuum casting machine. This machine is very large and is prohibitively expensive for the small businessman. It also has the disadvantage that in its use, the casting flask is cooled considerably, first, because it is initially outside of the chamber and subject to ambient air, and secondly, because the chamber is much larger than the flask and thus a longer time is required in forming the vacuum which itself rapidly cools the flask.
While each of these prior inventions has contributed to the casting process to various extents, there remains a need to improve upon the evacuation of air from the investment to thereby uniformly pull the molten metal into the mold. There is also a need to speed the vacuum process so as to cause less cooling of the flask. This cooling of the flask occurs at the rate of approximately 100.degree. F. for every minute it is exposed to the ambient air. Furthermore, the vacuum chamber and associated apparatus are often prohibitively expensive for the small businessman.